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The <netdb.h> header defines the type in_port_t and the type in_addr_t as described in in(3HEAD).
The <netdb.h> header defines the hostent structure that includes the following members:
| char | *h_name | Official name of the host. |
| char | **h_aliases | A pointer to an array of pointers to alternative host names, terminated by a null pointer. |
| int | h_addrtype | Address type. |
| int | h_length | The length, in bytes, of the address. |
| char | **h_addr_list | A pointer to an array of pointers to network addresses (in network byte order) for the host, terminated by a null pointer. |
The <netdb.h> header defines the netent structure that includes the following members:
| char | *n_name | Official, fully-qualified (including the domain) name of the network. |
| char | **n_aliases | A pointer to an array of pointers to alternative network names, terminated by a null pointer. |
| int | n_addrtype | The address type of the network. |
| in_addr_t | n_net | The network number, in host byte order. |
The <netdb.h> header defines the protoent structure that includes the following members:
| char | *p_name | Official name of the protocol. |
| char | **p_aliases | A pointer to an array of pointers to alternative protocol names, terminated by a null pointer. |
| int | p_proto | The protocol number. |
The <netdb.h> header defines the servent structure that includes the following members:
| char | *s_name | Official name of the service. |
| char | **s_aliases | A pointer to an array of pointers to alternative service names, terminated by a null pointer. |
| int | s_port | The port number at which the service resides, in network byte order. |
| char | *s_proto | The name of the protocol to use when contacting the service. |
The <netdb.h> header defines the macro IPPORT_RESERVED with the value of the highest reserved Internet port number.
The <netdb.h> header provides a declaration for h_errno: extern int h_errno;
The <netdb.h> header defines the following macros for use as error values for gethostbyaddr() and gethostbyname():
| HOST_NOT_FOUND | NO_DATA |
| NO_RECOVERY | TRY_AGAIN |
Inclusion of the <netdb.h> header may also make visible all symbols from in(3HEAD).
Default
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For applications that do not require standard-conforming behavior (those that use the socket interfaces described in section 3N of the reference manual;
see Intro(3) and standards(5)), the following are
declared as functions and can also be defined as macros:
| int | endhostent(void); |
| int | endnetent(void); |
| int | endprotoent(void); |
| int | endservent(void); |
| struct hostent | *gethostbyaddr(const void *addr, int len, int type); |
| struct hostent | *gethostbyname(const char *name); |
| struct hostent | *gethostent(void); |
| struct netent | *getnetbyaddr(long net, int type); |
| struct netent | *getnetbyname(const char *name); |
| struct netent | *getnetent(void); |
| struct protoent | *getprotobyname(const char *name); |
| struct protoent | *getprotobynumber(int proto); |
| struct protoent | *getprotoent(void); |
| struct servent | *getservbyname(const char *name, const char *proto); |
| struct servent | *getservbyport(int port, const char *proto); |
| struct servent | *getservent(void); |
| int | sethostent(int stayopen); |
| int | setnetent(int stayopen); |
| int | setprotoent(int stayopen); |
| int | setservent(int stayopen); |
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Standard conforming
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For applications that require standard-conforming behavior (those that use the socket interfaces described in section 3XN of the reference manual;
see Intro(3) and standards(5)), the following are
declared as functions and can also be defined as macros:
| void | endhostent(void); |
| void | endnetent(void); |
| void | endprotoent(void); |
| void | endservent(void); |
| struct hostent | *gethostbyaddr(const void *addr, size_t len, int type); |
| struct hostent | *gethostbyname(const char *name); |
| struct hostent | *gethostent(void); |
| struct netent | *getnetbyaddr(in_addr_t net, int type); |
| struct netent | *getnetbyname(const char *name); |
| struct netent | *getnetent(void); |
| struct protoent | *getprotobyname(const char *name); |
| struct protoent | *getprotobynumber(int proto); |
| struct protoent | *getprotoent(void); |
| struct servent | *getservbyname(const char *name, const char *proto); |
| struct servent | *getservbyport(int port, const char *proto); |
| struct servent | *getservent(void); |
| void | sethostent(int stayopen); |
| void | setnetent(int stayopen); |
| void | setprotoent(int stayopen); |
| void | setservent(int stayopen); |
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